To obtain a super-pure hydrogen by way of purification by diffusion of commercial hydrogen or isolation thereof from hydrogen-containing mixtures, use is made of hydrogen-permeable membranes made of palladium and palladium-based alloys. At the present time use is made of alloys containing up to 40% of silver (cf. FRG Pat. No. 2,305,595; U.S. Pat. No. 3,247,648; A. A. Rodina et al. Journal of Physical Chemistry, 1979, No. 5, 1350 /in Russian/).
A maximum hydrogen-permeability is inherent in alloys containing 7.6-9.6% by mass of silver. Also employed are alloys containing 18 to 25% of silver. To obtain a higher stability of the latter alloys, other elements such as indium are incorporated therein. (Cf. A. A. Rodina et al. Journal of Physical Chemistry, 1980, No.6, p.1551).
However, silver-containing alloys are less active in chemical processes associated with hydrogenation and dehydrogenation.
Other palladium-based alloys employed for hydrogen purification and containing gold, copper, boron, nickel, rhodium, cerium, yttrium and platinum either possess an insufficient mechanical strength (e.g. alloys with gold and cooper additions), or get broken under the effect of hydrogen and other aggressive media (cf. A. G. Knapton "Platinum Metals Review", 1977, V21 (2), p.44).
Incorporation into palladium, of additions of gold, copper and likewise silver lowers catalytical activity of palladium in dehydrogenation reactions. Incorporation of platinum additions makes palladium more durable, increases its catalytical activity, but considerably reduces the values of hydrogen-permeability of alloys. Furthermore, in the majority of these alloys two hydride phases .alpha. and .beta. are formed which when present together lower the selectivity of catalysts made from palladium alloys and serve as the reason of destruction thereof under the effect of hydrogen.
U.S. Pat. No. 3,238,700 Cl. 55-16 (1966) discloses a membrane for purification of hydrogen which is made of a palladium alloy containing 4.5% of ruthenium (by mass). Hydrogen-permeability of this alloy exceeds that of pure palladium, however, this alloy has but a short service life when operated in the atmosphere of hydrogen and hydrocarbon upon multiple cycles of heating and cooling and has a low selectivity in carrying out catalytical processes which is likely to be associated with the presence of two hydride phases (.alpha. and .beta.). During an operation of the membrane there occurs the transition .alpha..revreaction..beta. which results in breaking of the membrane. Furthermore, the presence of two hydride phases substantially lowers the selectivity of catalytical processes of hydrogenation and dehydrogenation due to different mechanisms and kinetics of reactions occurring at active centres of these phases.